


It's not a bug, its a feature.

by Drachenkinder



Category: Thor (Movies)
Genre: Bottom Thor, M/M, Sibling Incest, Size Difference, Spanking
Language: English
Status: Completed
Published: 2020-12-25
Updated: 2020-12-25
Packaged: 2021-03-11 02:27:29
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,547
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28317480
Author URL: https://archiveofourown.org/users/Drachenkinder/pseuds/Drachenkinder
Summary: Loki creates a potion to increase his strength so he can best Thor. Sure he had to use a few substitutions, but what could possibly go wrong?For thorkidumpste  and thoresque and the Thorki Secret Santa 2020
Relationships: Loki/Thor (Marvel)
Comments: 13
Kudos: 59
Collections: Thorki Secret Santa 2020





	It's not a bug, its a feature.

**Author's Note:**

  * For [thorkidumpster](https://archiveofourown.org/users/thorkidumpster/gifts), [thoresque](https://archiveofourown.org/users/thoresque/gifts).



It had started with a potion to enhance strength. Loki wanted, just once, to be the one to wrestle Thor to the ground. Though their rivalry had softened over the years, and Thor now treated him as an equal, it was still a bit galling to have every sparring session end with Thor pinning him down. That Thor was happy to deliver a few swats to his rump while he was held down only added to his frustration. It didn't matter that Loki liked the swats, or what they led to. It was the principle of the thing.

Loki was not terribly certain the potion would work. Some of the ingredients for the original brew where found only on Asgard, and their home world was long gone. He’d had to make substitutions, but so far he’d had luck doing so. Even if it didn’t have the full effect, it was bound to increase his strength a little. Nothing in the potion was actually toxic, though he had to admit powdered bull gonads were not his choice of aperitif.

Loki gave the potion a doubtful look, and poured it into an empty sports drink bottle. He’d wait until he was at their sparring site before drinking it. The effects wouldn’t last long and he wanted to be sure it wasn’t going to wear off mid bout. He gathered up his wooden knives and a couple of real sports drinks and set off into the woods behind his personal retreat. They’d started sparring there years ago when Loki was first regaining his strength and didn’t want to be the recipient of their people’s pity. They’d kept at it because Loki liked the privacy and Thor didn’t have to worry about putting his practice hammer through someone’s wall with a wild throw.

The afternoon was crisp and cold and a dusting of snow made the trees sparkle and the trail slightly slippery. Loki grinned. Thor might be stronger, but Loki was more sure footed. Even if the potion didn’t work, he would have the advantage today. Just ahead he could see his brother warming up by jogging about the clearing. Thor needed the warm up, today was his turn to settle disputes and he’d most likely been stuck in the throne since morning. Loki paused in the shadow of the trees, uncapped the bottle and chugged down the potion. He grimaced at the flavor and opened a real sports drink to wash the foul taste from his mouth. Thor spotted him as he strolled out of the woods and called a greeting. 

“Hey Loki,” Thor said, walking toward him with his hand out, “give me a drink.”

Loki swallowed his mouthful of the salty sweet mix and handed Thor the bottle. He could feel the thrum of the potion as it worked its way through his body. 

“I hope you are ready to be beaten.” Loki said. He took a few steps back, drew his blades and waited for Thor to finish drinking. 

Loki felt… odd… and his vision was disturbed, as if he were slowly drifting upward. He tried to take a breath and his chest was inexpiably compressed, his once loose shirt tight across his chest. All his clothes were too tight, painfully tight. The spell to alter his clothing was a simple one, and even in his distress he was able to make the necessary adjustment. He gasped a much needed breath and looked down at his wide eyed brother.

“Auðumbla's teats!” Loki swore. This was not how the potion was supposed to work. He wondered abstractly if it was the substituted ingredients or his own Jötnar blood that had caused the unexpected result.

“Loki?” Thor asked. “Are you trying out a new spell?”

“Yes.” Loki snapped. So much for sneakily beating Thor. He might be stronger, but there was nothing subtle about growing two feet taller and proportionally larger. But Thor didn’t seem to be upset. In fact he was circling around Loki as if sizing him up.

“This will be a challenge.” Thor said with a grin. “Clever of you to come up with a way to make our sparring more interesting.”

“What?” Loki started to say and then had to spin out of the way to avoid a hammer blow to his stomach. Luckily his body, despite its larger size, responded with its usual speed. His knives felt too small in his hands, as if he was fighting with a child’s toys. They were more a hindrance than a help and Loki dropped them to fight unarmed. He had to adjust his style to meet a smaller opponent, for now the top of Thor’s head only came up to the middle of his chest. Thor, however had faced much larger foes and had no trouble adjusting to Loki’s new size. 

It also didn’t help Loki that with his increased weight, the frozen slippery ground was no longer an advantage. On the other hand he was stronger, and the blows that did land staggered Thor, whereas Thor’s strikes hit a smaller area and were not as devastating as usual. He began to get the rhythm of the fight and smiled. Thor was right. This was more challenging. Quite frankly Loki found it fun to look down on his brother and have Thor running around trying to evade Loki’s longer reach. 

A nasty crack on his hip numbed his left leg and dropped him to his knees. Thor surged in, sure of victory, only to have Loki throw out an arm that caught him on his throat. His feet were still running forward as his head and neck came to an abrupt stop and Thor flipped up in the air to land flat on his back with the wind knocked out of him. Loki caught his wrist before he could recover and twisted his arm back and up until Thor was forced to turn onto his stomach and drop his practice hammer.

Loki pinned him down with his superior strength, laughing while Thor squirmed helplessly, trying to break free. His brother’s muscled butt was too tempting a target and remembering indignities he’d been forced to suffer, Loki brought his hand down in a resounding smack. Thor’s outraged howl was highly rewarding and Loki gave his rump two more sharp slaps. He was raising his hand for another when Thor said;

“You’re had your fun. Let me up.”

“I think not. I rather enjoy having you at my mercy.”

“Do you now?” Thor said and half twisted to look back at Loki. It wasn’t the expected anger or distress Loki saw, but a very different expression. Thor’s cheeks were flushed, his eyes sparking and a smile graced his mouth. Loki chuckled and ran his hand over Thor’s butt. 

“Why Thor,” Loki purred in a deep voice that made it more a rumble, “I think you’re enjoying your punishment.” 

Thor’s tongue darted out and licked over his lips. “Perhaps I am.”

“Then, since you are amenable, I don’t see any reason to stop.” Loki he sat up and crossed his legs. He patted Thor’s butt. “Unless your pride is getting in the way.”

It was easy to pull an eager Thor facedown over his lap, his hips on one leg and his shoulders on the other. Thor made a sound halfway between a groan and a moan and Loki rubbed his hand up and down his brother’s back. 

“You always have been too prideful. A lesson in humility would not be amiss.” 

Loki rested his hand on Thor’s back. He slide the workout pants down his brother’s hips and then his boxers, baring his lightly pinked rump to the frosty air. 

“I? Prideful? Truly Loki If anyone is too full of themselves.. OW!”

Loki chuckled and admired the red handprint on his brother’s rump. 

“You seem to have forgotten who is in charge, Love.” Loki gave him another swat that made his butt quiver.

“UH! I don’t suppose an apology will make amends?”

“Not in the slightest.” Loki said punctuating each word with a smack. He cupped and squeezed Thor’s ass cheeks, enjoying how his hand could now fully cover each firm globe. “But you are certainly welcome to make the effort.”

“I’m not feeling significantly motivated at the moment.” Thor said and wiggled his hips in invitation.

“Then I shall provide the impetus to get you in a more repentant frame of mind.” His hand came down on Thor’s rump in a steady rhythm, each hot slap layering the heat and turning his brother’s rump from soft rose to blushing red. Loki’s rapid breath told of his own arousal.

“Nice to know we share a kink,” Loki panted. “though you’ve never been interested in being on the receiving end before.” He concentrated on the underside of Thor’s bottom, where he’d feel Loki’s hand every time he sat down.

“You’ve never been this large before.” Thor admitted.

Loki glanced at Thor’s furiously blushing face and chuckled again. “So that’s how it is, hmmm? You like feeling like a misbehaving boy?”

Thor turned his head away to hide his expression, but he couldn’t hide his erection, which was digging into Loki’s thigh.

“Don’t worry, _little_ brother,” Loki said, happy to use the descriptive for once on Thor. “I’ll see you pay well for your every misdeed.” 

With that he swung his hand up and brought it down with a resounding smack on Thor’s butt. The result was a sharp gasp out of his brother and a darker handprint on his reddened rump. Loki felt a tightening in his own groin at the sight and sound and quickly repeated his action. Thor actually whimpered this time and Loki felt giddy with a combination of arousal and power. He’d never been much into giving a spanking before, but seeing Thor’s excited and submissive response was making his heart pound. More than his heart, as his cock pulsed with inflowing blood. 

“You’ve been a very wicked young man, Thor.” Loki said and his hand slapped again and again on Thor’s butt. His handprints overlapped with each stinging slap, quickly turning the already tender skin a burning deep crimson. Even more gratifying was Thor’s low cries and his squirming. Loki decided his brother could stand a little more and again smacked the underside of each cheek, this time with harder blows.

“Oh fuck!” Thor cried as his hips were forced against Loki’s thighs, with each slap. 

Loki paused, panting, an evil grin on his face. He bent over Thor to whisper in his ear. “Don’t you even think about spilling on my leg.”

“Then stop,” Thor panted, “because I’m close.”

Loki laughed and it was a wild sound. Thor shuddered to hear it.

“Please, Loki.” he pleaded.

Loki took a deep breath and calmed his racing heart. He stroked Thor’s rump with a gentle hand. “As you wish Beloved.”

“How do you hold off so easily?” Thor asked.

“Practice brother. In time you too will learn to control this basest of impulses.”

“I think I look forward to acquiring this new skill.”

“You’ll have to be a quick study, the potion will wear off in an hour.”

“Oh.” Thor said with disappointment. “You can’t make more?”

“I can, but it will take several days. I’ll have to buy more of the ingredients. But you should know before you ask that of me, that taking potions is not something a sorcerer should do on a regular basis.”

Thor made an exasperated sound and Loki took that as a cue to slap his rump again

“Don’t be so greedy.” Loki said as he heated his brother’s sore bottom to a hotter burn. “You’re acting like a spoiled, ungrateful brat.”

“I don’t care!” Thor panted.

Loki grinned. Thor had just manipulated Loki into playing the game by his rules. Loki didn’t mind. He was enjoying being the strict disciplinarian as much as Thor was enjoying his supposed punishment. He spanked Thor’s butt harder and Thor actually yelped.

Loki had to stop and take a few quick breaths so he didn’t spill at the sound. He pulled Thor’s hair to wrench his head back and growled. “You are a wicked, self-centered imp and I want, very much, to fuck you.” He interspaced his words with sharp spanks that made Thor’s ass burn.

“Then do it Loki!” Thor rumbled.

“Norns!” Loki swore. “I’ll tear your apart.”

Thor chuckled. “You aren’t that much bigger then you were, and I’ve always managed your cock before.”

“That sounds like a challenge.” Loki said. He concentrated and with a green glow of seidr a jar appeared in his hand. He unscrewed it, set on Thor’s back and dipped out a generous dab. Spreading Thor’s bruised cheeks with one hand, he rubbed the slick cream over his tight furled hole.

“Ah.” Thor moaned. He gave a louder moan when Loki pushed his finger inside. It was thick enough that Thor began to question his ability to take Loki’s cock, right up until Loki pulled it back out. 

“No!” Thor said.

Loki gave his butt another slap. “If you want my cock you need to move off my lap, _little brother_.” He purred, turning the endearment into a taboo that sent Thor’s blood racing. 

Thor clambered off Loki’s lap, and crouched in front of him, lowering his shoulders to rest his head on his folded arms. “Like what you see?” Thor said. 

“Very much.” Loki replied. He freed his cock and gave it a stroke, spreading the cream from blushing tip to dark root. “Still think you can take this?”

Thor swallowed. Loki’s shaft was half again as big as it had been. It was enough to make him shiver with fear and desire. And with the cold. Now that Loki was not blocking the chilly wind he was exposed in his most vulnerable places. 

“I want to try. Go slow and let me get used to it.”

“I will. But not here.” Loki said. He stood up. “I don’t want to risk you getting frostbite on your lovely cock.”

I’m not going to get..”

“You aren’t arguing with me are you?” Loki snarled and put a booted foot between Thor’s shoulders. It was a ridiculous move if was actually trying to bully Thor, for it left him off balance and all Thor had to do was sit up, to knock him back. 

But Thor gave a low moan instead and said. “No.”

“Good. I’d hate to think you need even more correction.” Loki flexed his hand. “My palm is starting to burn and I’ll have to resort to my belt if you do.” He ground his foot to press Thor’s shoulders into the frosty earth. 

“I’ve learned my lesson.” Thor said. He didn’t want to risk the belt. At least not this time.

Loki let him up, took his brother’s hand and in a flash of light teleported them both the short distance to his home. Thor staggered at the feeling of rapid movement abruptly stopped. Before he could recover his equilibrium, Loki shoved him onto his back on the bed. His hands came down on either side of Thor's waist and he bared his teeth in a wolf’s grin.

“These clothes are in my way.” Loki said, and both of them were stripped naked in a wash of verdant magic. 

Loki lowered his mouth to Thor’s and kissed him slow and deep. The softness of Thor’s lips surrounded by the roughness of his beard was familiar, but the smaller size felt strange. Loki had had petite lovers in the past. Not everyone on Asgard was six feet tall. But this wasn’t some plump little woman or short willowy man, this was Thor. Hard muscled and broad shouldered and every inch a warrior. Only now, Loki was large enough to manhandle him. He was half mad with desire and the physical power he held over his brother. His kisses were rough and demanding. Thor’s lips parted, opening to him, his legs spread and his knees lifted and clamped against Loki’s sides. 

Loki pulled back, and Thor swore at him. “You bastard.”

Loki laughed. “You are such a slut, brother. I want to watch my cock going into that greedy ass of yours. Pull your knees up higher.”

Thor put his hands behind his knees and complied, putting himself on display for his brother’s avid gaze. Loki pressed his knees further apart and higher still. He licked his lips at the sight of Thor’s thick cock leaking on his belly, his heavy balls and his bruised spanked butt. He took his own cock in hand and pressed the head to Thor’s oil slick entrance.

“Your ass looks like a ripe plum, and I intend to split it open.”

“Loki, shut up and fuck me!” Thor demanded.

Loki’s reply was a slow thrust of his hips that stretched Thor’s rim wide around the thick head. Thor gasped and Loki paused, trembling with the effort to keep from ramming himself all the way in.

“Keep going!” Thor panted. 

Loki nodded and pushed his cock deep into the tight, heated grasp of his brother’s body.

“Fuck!” Thor cried and Loki answered “Norns!” His eyes were on Thor’s belly and the way it bulged, outlining the path of his cock as into his brother’s body. Thor’s eye’s followed his and widened. 

“Damn!

“I’m not hurting you am I?” Loki said, hoping he wasn’t. He forced his eyes away from the entrancing sight and met Thor’s eyes.

“No. It’s intense but not painful.” Thor let go of one knee to run his hand down the bulge. Loki groaned. “Like that?” Thor inquired.

Loki nodded. “It’s the most obscene thing I’ve ever seen.” He grasped Thor’s knees himself, and rocked his hips back. “Do it again. Stroke my cock while I fuck your belly.”

Thor nodded and grasped his own cock. When Loki pushed back into him, Thor pressed done the length of his rising stomach with his other hand. Loki made an animal sound and jerked his hips back and then forward. Thor groaned at the cry and the pleasure of being filled so impossibly full. Sweat beaded his skin and he squeezed his cock and then worked his hand up and down the shaft. Loki took this as permission to go ahead and rocked his hips in a slowly increasing tempo. Loki was sweating too, on fire with hunger and high on Thor’s heated response. He bent down to capture Thor’s mouth and they panted and kissed, licking and sucking and nipping each other's lips.

Thor was furnace under him, sweat slick skin sliding on his own and oil slick channel hot and tight around his thrusting cock. Loki melted joyously into the sapphire flames of Thor’s eyes. He fucked faster now, and Thor worked Loki’s huge shaft with every thrust. He squirmed his ass against Loki’s hips when Loki was sheathed inside him, clenched around his length and rubbed his hand up and down his own belly to increase the pressure.

“Harder!” Thor commanded, abandoning any pretense of submission in his need to feel Loki unleash his full strength. 

“Yes. My. King!” Loki said through clenched teeth. Loki pounded into Thor’s ass, his hips smacking the bruised globes. “I’m going to cum so hard up your ass you’ll taste it.”

“YES!" Thor howled, his hand frantic on his own cock. "DO IT! Fill me up! Ah! Ah!” Thor arched, his hips jerked and Loki felt the hot splash of his brother’s seed on his chest.

Thor’s muscular ass clenched like a vice, milking Loki’s driving cock. Loki growled and set his teeth into Thor’s shoulder, hard enough to taste blood. His balls pulled up against his groin and he spilled, shuddering in a climax of pleasure and power. His magic swirled and poured into Thor with each pulse of his cock, filling his brother's belly with intent and carrying his seed deep into the secret places of Thor's body.

Loki collapsed over Thor, shaking, over stimulated and exhausted with the release of passion and seidr. The room was spinning and shrinking, his head pounding, and his vision strobing as he fought for breath. He shut his eyes and trembled as Thor stroked him. He rested on his brother’s broad chest and the big hands stroked down his back. Tears fell from his eyes and pooled under his cheek as he sobbed.

“Love… you…” Loki managed.

“I know baby.” Thor said. “Take it easy now. Rest love.”

Loki nodded or tried to. He wasn’t sure if anything responded. He could feel Thor’s powerful arms around him and the dampness of sweat and seed and the rise and fall of his brother’s chest and the steady beat of his generous heart. “Back to normal size” his mind noted against the background of too much emotion and an exhausted haze. 

“Loki, are you alright?” Thor asked.

“Uh huh. Good. More than. You?” Loki said. He was tipped onto his back and lay boneless on the bed.

“I’m feeling a little hollow at present, but I’m sure that will resolve on its own.”

"It will in time." Loki chuckled without opening his eyes. “Size whore.”

“Well,” Thor said, cupping his chin and kissing him gently. “I did marry a frost giant.”

**Author's Note:**

> I hoped this hit the spot. Happy holidaze.


End file.
